The Vestibular Auto-Rotation Test
The VAT tests the accuracy of the vestibulo-ocular reflex. A patient, monitored via electrodes, moves their head back in forth first in the horizontal plane and then in the vertical place. We will commonly call this a yes/no test.
The VOR is measured by having the patient keep their eyes focused on a small target while the head is moving, either vertically or horizontally. When the VOR is working in its normal fashion, the relationship of the eyes and the head are 180 degrees out of phase. In other words, for objects to stay still on the back of the retina, when the head goes hard right, the eyes must go hard to the left.
We like the VAT for a number of reasons:
- Pre and post therapy assessments are given quantifiable measures.
- The generalizabilty of this test is excellent. For example, patients measured for VOR issues in rotary chair configuration are strapped into a chair where they are physically accelerated and stopped. The head and inner ear are moved rather than the patient moving the head volitionally. Granted, this is a pure test, however, the yes/no dynamic of the head movement measured by the VAT is much more likely to be duplicated when the patient leaves the clinic.
- VAT mismatches or instances where the test reveals poor synchronization between the head and eyes will explain unsteadiness in patients where VNG results and posturography results are normal.
Because of the variables involved with neck and eye movements, the Werner Institute runs numerous trials of both the horizontal and vertical VAT. The results are averaged and referenced against normalized ranges. Occasionally the VAT is contraindicated due to stiffness/neck pain or inability to perform the head movements.